Polytetramethylene ether glycol (hereinafter referred to as “PTMG”), a typical kind of tetrahydrofuran polymer, is generally used as main materials of spandex, a plasticizer and an emulsifying agent due to its ductility. Poly-THF is prepared from THF, and especially, by using a heteropolyacid catalyst. For example, a process for preparing Poly-THF using heteropoly acid as a catalyst is disclosed in U.S. Pat. No. 4,568,775, No. 4,658,065 and No. 5,416,240. In comparison to the two-step process for preparing polymer from tetrahydrofuran (U.S. Pat. No. 6,979,752), only one-step process is provided by these inventions. However, this process leads to a low polymer yield.
A reaction mechanism for preparing polymers by using THF in the presence of acidic catalyst is also known (Catalyst Today 2002, 73, pp 29). THF polymerization reaction comprises three steps of Initiation, Propagation and Termination, and is divided into one-step reaction and two-step reaction depending on the kinds of reaction terminators. Commercially, a heteropoly acid is used in the one-step THF polymerization process, and in the reaction process, THF is changed into Oxonium ion in the presence of a catalyst, thereby serving as an initiator. Therefore, the more the concentration of the Oxonium ion is increased, the more active the polymerization reaction becomes, thereby resulting in a higher reaction yield. The process for producing Oxonium ion is already known (Solid State Ionics, 2001, 139, pp 281). In order to produce THF Oxonium ion, iodine (I2) is added to produce iodine cation, which is then combined with oxygen to be converted into the THF oxonium ion. Such process for forming the THF oxonium ion leads to an assumption that the yield of the polymerization reaction would be increased by putting an additive that can be easily ionized into positive and negative ions, such as iodine (I2), due to activated initiation step of the polymerization additives. However, elements like iodine (I2) discolor the Poly-THF, thereby deteriorating properties of the Poly-THF, though they have an advantage of activating a polymerization reaction. Thus efforts have been made to develop an element that activates a polymerization reaction without changing the properties of the Poly-THF.
The hydronium ion (H3O+) allows positive ions to be formed easily, as the hydrogen ion is attached to the water molecule. And after the detachment of the hydrogen ion, remaining water is used as a reaction terminator of polymerization without any effect on polymers after the reaction. The inventors of the present invention have paid attention to this point to provide a method for increasing yield of the polymerization by adding hydronium ion as a reaction initiator in the initiation step.
The object of the present invention is to provide a method for improving THF polymerization yield by increasing concentration of the hydronium ion in water used as a reaction terminator when polymerizing THF in the presence of a heteropolyacid catalyst.
In order to achieve the above object, the present invention provides a process characterized in that: THF is used as a reactant in the presence of a heteropolyacid catalyst; and a reaction initiation step is activated by increasing concentration of the hydronium ion in water used as a reaction terminator.
Polymerization yield may be improved by producing Poly-THF according to the present invention, compared with the conventional method of adding only water as a reaction terminator.